The present invention relates to a process for preparing an aluminum-free boron containing zeolitic material having an MWW framework structure, referred to hereinafter as BMWW, wherein after the hydrothermal synthesis of the precursor of the BMWW, said precursor is separated from the mother liquor by filtration in a filtration device. Prior to said filtration, the pH of the mother liquor is suitably adjusted. Further, the present invention relates to an aluminum-free boron containing zeolitic material comprising the framework structure MWW, an aqueous suspension which contains as-synthesized BMWW precursor primary crystallites, and a filter cake containing as-synthesized BMWW precursor primary crystallites. Yet further, the present invention relates to a use of the aluminum-free boron containing zeolitic material comprising the framework structure MWW.
Boron containing zeolitic materials of zeolite framework structure type MWW (BMWW) are used as precursor compounds for the preparation of titanium containing zeolitic materials of zeolite framework structure type MWW (TiMWW) which in turn are mainly used as oxidation catalysts, in particular as epoxidation catalysts. Such oxidation catalysts are employed in industrial-scale processes, and consequently, there is a need for economically advantageous processes for the preparation of these TiMWW catalysts and the respective BMWW precursor which have to be prepared in large quantities.
The process for the preparation of BMWW usually includes the hydrothermal synthesis of a BMWW precursor starting from a silicon source, a boron source, and a template compound allowing to obtain the BMWW precursor from the hydrothermal synthesis. The thus obtained mother liquor containing the primary crystals of the BMWW precursor is subjected to filtration and usually washing in order to separate the BMWW precursor from the mother liquor. Such filtration is described, for example, in WO 03/074421 A1, in Example 1. According to this teaching, the solid product obtained from hydrothermal synthesis is separated by filtration and washed with ion exchanged water. The same disclosure can be found in Example 1 of WO 03/074422 A1.
Now, it was found that this filtration of the BMWW precursor usually takes considerable time and thus represents an unfavorable step, especially in case large quantities of the BMWW and thus of the BMWW precursor are to be produced. Further, once the respective filter cake has been obtained, it was found that washing this filter cake represents yet another very time consuming step of the process since the filter cake usually is very compact, exhibiting a very high washing resistance. Both the problems regarding the filtration of the mother liquor containing the BMWW precursor and the usually applied further step of washing the respectively obtained filter cake containing the BMWW precursor lead to a major disadvantage of this undoubtedly established process.